Cable tension governor



April V21, 1942.

J. sTuRGEss CABLE TENSION GOVERNOR Filed Ja.n. l5, 1940 IAlII V' Lidi,"

IN VEN TOR. JoH/v ST1/@SESS an aircraft fuselage or frame, or

Patented Apr. 21, 1,9424

, 2,280,105 t CABLE TENSION cfOvEmvoR` Glendale, Calif., assignor to I lLos Angeles,y Calif., a corporat John sturress.

Sturgess, Inc., tion of California Applicationlanuary 13, 1940, SerialNo. 313,802 t 11 claims. (ci. 'a4-501) This invention relates to controlcables of aircraft and other structures wherein pairs of cables undertension are employed for moving a work member such asa rudder, aileron,engine controls, and other auxiliaries, to various positions back andforth from the manipulation of a control element or member operated bythe pilot or other operative.

The principal object of the invention is to provide meansV forautomatically maintaining any predetermined or initially set tension insuch a pair of control cables; y

A further object of the invention is Ato provide means as immediatelyabove 'set forth which will automatically maintain the initially settension in such a pair of cables regardless of stretch in the cables, orshrinkage thereof or apparent shrinkage or contraction due to expansionor elongation of the supporting structure, ysuch as wear of cables,guide pulleys, distortion of brackets, etc.

A further object of the invention is to provide an automatic cabletension control apparatus which does not require the partingv orseverance of a cable or cables in order to operate or be placed at anyintermediate point as an element of the cables length, but such anapparatus which will operate on a pair of integral or continuous cablesboth at all times permanently connected at their ends respectively tothe work member and to the pilot control element.

A further object of the invention is to provide an apparatus asaboveoutlined which will not impair or interfere with manual or pilotcontrol at any time, even if the automatic apparatus itself should failor become inoperative.

' A still further object ofthe invention is to provide an automaticcable tension maintaining apparatus which will maintain the initial settension in a pair of control cables without being affected by temporarychanges in tension of one of the cables as compared with the other dueto operating the control, wind reactance on the work member, etc., andwhich would greatly increase the tension on the pulling cable of thepair'while slacking olf the tension on the opposite cable of the pair.

Other features and advantages of the invention will appear in thefollowing description and accompanying drawing:

In the drawing:

Fig. 1 is a general layout showing a pair of control cables connected atthe ends respectively to the work member and to the pilot controlmember, with my automatic tension control Department of Commerce, andother'authorities apparatus ly operated. Some of the mechanism is shownpartly in section.

Fig. 2 is a detail showing an electric motor actuator in place of the inFig.` 1.-

Fig. 3 is a reduced size drawing showing a modified arrangement of thetension adjusting pulleys. Y

Before describing the drawing in detail an outline of the requirementsto be met and general functioning of the invention will be givenhydraulicv actuator shown so as to make the operation of the elementsshown in the drawing more readily understandable.

Aircraft control-cables are rigged in pairs respectively at one end eachat opposite sides of the pivotall point of a rockable, plots controllingelement, such as a pedal, wheel, or stick, and at the other ends to therockable work member or control surface of the craft, the cables beinginitially made equally taut to insure motions of the pilots controlapparatus being definitely transmitted to the control-surface or otherwork member. The degree of tension of the cables isn set out inengineering specifications, based on requirements. If rigged too tight,undesirable resistance is imposed on the pilot's actions, and if tooloose the response of the control-surfaces is sluggish and unreliable.Furthermore, the vibration-frequency of the surface members is aected bythe cable-tension, and this frequency is a matter of great importanceand subject to rigid specifications and test.

But even if the cables are correctly rigged in the factory or at thehanger, the tension will subsequently vary over a wide range due to theunequal expansion, under varying temperatures, of the duralumin airplanestructure and the steel cables. Deflection. stretch of the cables andwear of guide pulley structures also affect the cable-tension, theseinfluences defeating attempts to maintain the initially rigged specifiedtension. Of these inuences, temperature changes are the most potent.

No practical solution of this difficulty has heretofore been found,thoughits' seriousness is recognized. Such research as has been made hasbeen in the `direction of thermostatic apparatus, as being the mostobvious remedy. But thermostatic apparatus has thus far been foundimpracticable for use on. airplanes, for several reasons, andparticularly as difhculty arisesas to 'where toy place the thermostat sothat the locaapplied to the cables, and hydraulicaltion shallrepresentnthe average temperature of the airplane. Other efforts havebeen in the direction of sheathing the cables with Dural.

My invention solves the problem by using the tension of the cablesthemselves to actuate means for increasing or decreasing their tensionas might become necessary to maintain it constant. But in omtccomplishthis a-great dfliculty had to be overcome, for 'while we speak of therigged tension (that is the tension when the airplane is on the ground)yet that tension does not prevail during flight. The tension isconstantly varying by reason of the reaction of the control surfaces toair pressure.

Two cables are Aused for each such surface on opposite sides of therocking pivots, rigged to a definite tension when the airplane is notinflight. But during flight one of the pair is subject to a highertension, and the other to alower tension, according to the degree ofmovement of the control surfaces and other causes such as speed, wind,rate of banking, turning, etc. In extreme cases the loaded c able willcarry a tension several times the initial tension, w le the unloadedcablemay be substantially slack. It will, there- 2 fore, be seen thatany automatic tension control method actuated by the existingcable-tension itself must provide for the foregoing condition,-

at rst seemingly impossible.

It was, therefore, necessary to devise apparatus which would function inresponse only to the initial tension component of the total tension andnot function in response to temporary additional loads (live loads)occasioned by moving the pilots controls even if the temporary changeswere of long duration,possibly the entire period of the flight, It mustalso be irresponsive to the operative travel or movements of the cables.

My invention accomplishes all this in a simple manner, and itseffectiveness has been proven by actual tested construction.

'I'he invention comprises a series of guide pulleys and lever pulleysmounted in a special manner in relation to a pair of control cables, and

'a power actuator, preferably hydraulic or electric.

The arrangement is such that movement imparted to one or more pulleys(hereafter vcalled the tension-adjusting pulleys) by the powei actuatortightens or slackens the cables according to the direction of movement.The mounting of another one or more pulleys (hereinafter called thetension-indicating pulleys") is such that variation in the tension ofthe two cables acting on these latter pulleys causes movement of thelever carrying these pulleys, which movement controls the movements ofthe power actuator. If an electric motor is used for power, the movementof the pulley lever will actuate contacts. If hydraulic, the saidmovement will actuate suitable distributing valves. When the poweractuator moves the tension-adjusting -pulleys-either to increase ordecrease the tension in the control cables, this increase or decrease intension is at once felt by the tensionindicating pulleys so that when itarrives at a value equal to the total initially set tension of the twocables, the resulting movement of the lever carrying thetension-indicating pulleys shuts off the power actuator, or ratherbrings it to neutral position with the tension-adjusting pulleys lockedin their new position until the actuator is again moved either tofurther increase the tension or reduce it, as the conditions (effectivecable pressure on the tension-indicating pulleys) may prescribe, tomaintain the initially set tension.

Now with reference to the drawing:

No detail ofv the aircraft structure, nor the usual guide pulleys forthe cables are shown, but only such guide pulleys as contribute to theoperation of the invention, it being understood that the cables may berun through various turns over any number of other guide pulleys as maybe required to operate any desired rockable moving part or surfacemember of the craft.

The control cables shown are designated I and 2 and are indicated aspermanently connected at one end each to a rockable control element 3 atopposite sides of its xed pivotal support 4, and similarly at itsopposite ends to a. rockable work member 5 at opposite sides of itsflxed pivotal support 6. Turn buckles I or common threaded anchor boltsatthe end of the cables, or their equivalent may be used for adjustingthe cables to the initial tension desired.

A series of grooved guide pulleys, C, C, C, C and L, L, are shown spacedequally from opposite sides of a center line X between the Itwo cables.

The idler guide pulleys bear against the outermost sides of the cablesvand are each revolvably supported on pivots 8 fixed in relation to thebody of the aircraft, and against the thus deflnitely spaced cables mycontrol operates. Some of the guide pulleys shown may of course be those-ordinarly required for operative guidance of the cables. Y

The tension-adjusting pulleys 9, l0 are pivotally mounted on a bracketlever A pivoted centrally at B to a fixed point. The center line of thebracket, through the two pulleys, lies at an angle V of approximately 45degrees tc the cables. and each pulley is in contact with oppositecables. The pivot, B, is midway between the two pulleys. The four xedidler guide pulleys, C, are arranged on both sides of the vpivotedbracket A. The spacing of the six pulleys relative to the pulleys 9, I0,being such as to create an'oset in each cable, thereby shortening theiroverall length an amount depending on the angular position of thepivoted bracket lever.

Movement of the pivoted bracket lever is accomplished by the poweractuator, shown in Fig. l as a double acting hydraulic cylinder Econtaining a piston Il at the inner end of a piston rod l2.

Since the required movement of the bracket lever to vary the cabletension is small, and the movement of the hydraulic piston (or electricmotor, if used) is relatively long,

ducing mechanism is necessary. 'I'he simplest,

and preferred form'is a wedge, attached tothe tor). This wedge is shownat piston rod (or reducing motion if electric-mo- D slidable on a fixedsupport I3, anda shoe, or roller, F, riding on the wedge, transmits thereduced motion to the pulley-bracket by means of suitable links, G,while other links, H, pivoted at one end to the roller'and at the otherend to a xed point Il hold the shoe, or roller, in proper position whilepermitting motion of the roller substantially normal to the wedge.

The degree of offset to the cables must be such that maximum expansionof the fuselage permits some of the oifset to remain when thetensionadjusting pulleys are in the tight cable position, while thedegree of -motion imparted by the wedge to the pulley bracket must besuch asl to provide for the full range lof expansion as well asVsuillcient provision for wear on stretch of cables.

a motion rei dueltofthe varying locked, thus h olding f the conditionwhen The mountingor instemmen-indicating pulv leys lB-IB is an importantpart of my invention sincel this mounting solves the problem set uploads on the cables. These pulleys l and `I6 are `mounted on abracketlever,` K,pivoted at M between fixed pulleys, C and L, so thatone is in contact with each of the cablesof a pair.`

The center line of the bracket lever K, taken throughjfthe two pulleys,normally lies at about anan'gle W of approximately 45 degrees to thecables. Thisy bracket-lever is pivoted at M, a iixedpivot like bracket,but instead, the pivot M movable links, N, set parallel to pivoted to` aAfixed point l1.

the cables and Thus the pivot, M,

not the tension-adjusting pulleyis carried by cannot move in thelongitudinal direction of. the

cables, but is free to move at right angles thereto. An extended arm P,lof the bracket-lever K standing` at about right angles to the cables ispivotally connected by a link, Q, to a balanced piston-valve J, whosemovement controls the movement of the hydraulic piston. sion spring, R,attached to the opposite end of bracket-lever K tends to create onsetsin the cables, in opposite directions, which offsets are a measure ofthe tension in the'cables, as determinedby the tension of the spring.The onsets should be relatively small, and\the spring short andstin, soas not tc introduce a resilient elementin the cables. j In the operationof uid under pressure from any suitable source such as a constantoperating oil pump not shown, carriedon the aircraft, is admitted to theinlet `port I9` toithe central reduced portion of the pistonvalveJ whichnormally seals on both ports 2|i,"v2`| leading respectively to oppositeends of the cylinder E. A` movement `of the piston valve J from thecentral po"tion simultaneously opens either port or 2|, as the case maybe, to exhaust `port 22, and opens the other port tothe liquid underpressure from the piston is impelled in one direction by the incomingliquid at one side of the piston, while A stout teninlet port I9. Thusthe load on one cable ofthe pair,

through the linkage described, moving it from its mid-position to theright and opens the valve .ports to admit fluid pressure to the righthand side of the piston, and release to exhaust the oppcsitevside. Theresulting movement of the piston, and attached wedge and linkage,rotates the pivoted bracket, A, so as to diminish the onset in thecables sufficient to restore the tensionrto its original value. As thisoccurs the pivoted bracket, K, responds by `returning to itsmid-position, and the mechanism again `becomes hydraulically locked.

If the initial tension decreases, the opposite actions occur, with thesame result.

The foregoing description of operation, disregards any intermittent liveload on the cables, such `as would be set up inservice.

If such additional load occurs, it will increase and diminish it on theother cable. If the initial tension in both cables is 100 lbs., and thepilot applies a load at his controls to increase the tension onjtheloaded cable to 15G lbs., the lopposite cable will the hydraulicactuator, licl-l have its tension diminished to exerts a load of 200lbs. on one of the cables, the tension on the two cables will be 200lbs. and 0 lbs. respectively, and neither of these conditions l(or anyother load that might be applied) must cause the governor to operate. f

The tighter cable will have its onset at the tension-indicator pulleysI5 and i6 diminished,

but the onset of the slacker cable will be in'- creased .because thespring R applied its effort merely to separate the two cables, and thepulley bracket-lever K as a whole, assumes a position4 midway betweenthe two offsets-the lesser and the greater, which it can readily dosince the links, `N,and Q, permit such movement.` But the movement ofthe bracket K permitted by the link the liquid from the other sideescapes through y exhaust port 22 back to the pressure source for useagain.

, In operation of my. cable tensioning governor as above described, whenno live load is on the cables, and they only are exposed to theirinitial, or rigging tension, the onsets in the two cables aresubstantially equal and the pulley bracket K, or rather its pivotalpoint M- lies in mid-position between the cables, and the linkage of thebracketv to the piston valve J is such that the latter is also inmid-position, and at'whichboth fluid passages to the two ends of thecylinder E are closed, so that the piston is hydraulically ley-bracketlever, A, in a fixed position. This is the initial tension is correctand even on both cables. To insure this position of the piston valve ofthe cables, means is provided for adjusting the tension of spring R,here shown as an adjusting nut S bearing against` a xed s top T andengaging a threaded anchor bolt U to which the end of the spring ishooked.

If the initial tension of the cables increases, such as by expansion ofthe fuselage etc.',;from heat, the component of the triangular onset,acting against the spring, preponderates over the latter, and slightlyrotates the bracket K. This motion is transmitted to the piston-valve,

under the initial tension Q without moving the valve J does not changethe angular position of the bracket and Aconsequently does not move thevalve or cause spreading movement of the tension adjusting pulleys.

If' load is applied on the opposite cable of the pair the same enectoccurs, except in this case the pulley-bracketalso moves in the oppositedirection, at right-angles to the cable.

A remaining condition to be considered is the travel of the cablesduring operation of the controls by the pilot. .Such travel simplyrotates the pulleys without affecting the position of thepulley-brackets, and consequently does notcause the governor to operate.

Since control cables are so vital to the safety of an airplane,subjecting them to the influence of any automatic apparatus involves therequiree ment, that failure of the automatic apparatus, however remoteand improbable, must not render the cables manually inoperative, butthey must at all times be under full manual control whether theautomatic tension governor works or not. In my automatic cable tensiongovernor as described and shown, if, for example, the hydraulic pressuresupply fails, or the pipe-lines break, the governor will be renderedinoperative but the cables will remain intact and always under manualcontrol of the pilot, and the onset in the cables caused by the tensionadjusting pulleys lwill remain (thus preventing the cables slackening)because the wedge is a vself-locking device, so that reliance is notmade on the hydraulic locking of the piston.

The necessary pulleys and brackets and in the governor are no morevulnerable thanthe numerous` pulleys and brackets in. present cableinautomatically wedge operate againstand bearings are at both sides Inthis showing the power cylinder E is posistallations required to lead.the cables from the' the point of operation extension 29l of the shaft30 of a reversing elec-` tric motor 3l. Threaded shaftl 30 has its outeru end left unthreaded and is rotatably supported.

in a bearing 32.

Motor 3| is suitably fixed in position on the aircraft structure and isequipped with a suitable electric brake 31 of the well known type whichclamp the revolving parts against motion whenever the motor circuitcurrent is broken for instant stopping thereof, and releases the rotorthe moment the circuit is closed.

The motor is provided with a suitable reversing switch to the other waymovement of the end of lever P. In the drawing this reversing switch isenclosed in a housing 33 and is indicated as a. suitable switch withslidable actuating rod 34 extending out of the housing and pivotallyconnected to lever P of .ment of lever P in either direction fromcentral bracket K, all so that upon moveor initial position the motorwill revolve either to the rightor left as-thecase may be to carry thenut 23 in either-direction to properly rock bracket A for restoring theinitial cable tension,

and when the original tension is restored, the reversing switch is atneutral center position. Numerous variations of the arrangement .may bemade by those skilled in the art. Y,

A modification in the mounting Aof the tensionadjusting pulleys 9 and I0is shown in Fig. 3'

and wherein the two pulleys are forced apart to spread and tension thecables by a double wedge block D' directly connected to the pistoniod l2of the power cylinder E for moving the Wedge back and forth alongsuitable fixed guiding rollers or blocks 40. The outer edgesv of thebearings 42 in which the axles of pulleys 9 and l0 revolve, and thebearings may be stabilized by pivoted links 43 pivotally anchored attheir outer ends 44 toa Xed point. It is o! course understood that theWedge of the pulleys.

tioned between the cables I and 2, and its valve J (not shown) would ofcourse be positioned for connection to suitable operating linkage frombracket K as described for the showing of Fig. l.

Since the angular relation of bracket-lever K with respect to the cabletension is definite with a certain adjustment of spring R, it followsthat a pointer 23 extended from the bracket may be provided or thebracket linked to such a pointer at a remote point, to give a constantreading of the cable tension on a suitably graduated scale 24 ifdesired.

Having thus described my automatic cable tension maintaining governorand the manner of its operation as well as some of its modiiications, itwill be evident that various other modifications in its construction maybe resorted to without departing from the spirit of the invention, andany such variations are intended to be embraced in the scope of myappended claims.

be operated respectively by one, or

I claim:

1. An automatic cable tensioning apparatus comprising means movable inopposite directions for increasing or decreasing the tension in a pairof tensioned control cables depending on the direction of movement, adouble acting power actuator arranged for operating said movable meansincreasing the cable tension and in opposite direction for decreasingthe tension, movable controlling means operated by pressure ofdeflection of said cables controlling the actuation of said actuator,and means balancing said movable controlling means in position with saidactuator stopped when the tension of said cables is at a predeterminedpoint.

2. An automatic cable tensioning apparatus comprising means movable inopposite directions for increasing or decreasing the tension in a pairof tensioned control cables depending on the di-i and means foradjusting the tension value in said cables at which said movablecontroling means is balanced.

4. An automatic cable tensioning apparatus the tension oi against saidcables them under said initial tension, a power actuator said cables. iA

6. An automatic cable tensioning apparatus for a pair of initiallytensioned control cables, comprising spaced supports guiding rthe cablesin adjacent big'hts, a first rocking lever pivoted at a point between'said cables arranged to bear to normally deflect both'of operativelyconnected to said first rocking lever for rocking the same to increaseor decrease the movable means is in position of initial tension ofbearing against one deection of said cables, a second rocking leverpivoted at a point between said cables arranged to bear against saidcables, a spring urging said second rocking lever in directiondefiecting said cables slightly, a starting and 'stopping control onsaid power actuator, and means connecting said second rocking lever foroperating said control upon movement of said second rocking lever, dueto changes in initial tension of said cables.

a pair of initially tensioned control cables, comprising spaced supportsguiding the cables in adjacent bights, a rst rockingv cables slightly, astarting-and stopping control on said power actuator,

and means connecting said second rocking lever for operating saidcontrol upon movement of said secondrocking lever, due to changes ininitial tension of said cables, the

pivotal point of said second rocking lever being fioatingly mounted formovement tr-ansversely of the run of said cables..

8. An automatic cable tensioning apparatus for a pair of initiallytensioned control cables, comprising spaced supports guiding the cablesin adjacent bights, a first rocking lever pivoted at a point betweensaid cables arranged to bear against said cables to normally deflectboth of them under said initial tension, a double acting hydraulic poweractuator operatively connected to said first rocking lever for rockingthe same to increase or decrease the deflection of 4said cables, asecond rocking lever pivoted at a point between said cables arranged tobear against said cables, a spring urging said second rocking lever indirection defiecting said cables slightly, a starting and stoppingcontroll valve on said power actuator, and means connecting said secondrocking lever for operating said control upon movement of said secondrocking lever, due to changes in initial tension of said cables.

9. In the construction set out in claim 6, both of said rocking leversprovided with idler pulleys bearing on the cables.

lever pivoted at a point between said cables arranged to bearv deflectboth ofi ing a pair of control 11. In the 4construction set out -in,claim 6, means for adjusting the tension of said spring to balance anydesired initial tension in said cables with said second rocking'lever inposition for stopping said power actuator.

12. In an apparatus for automatically tensioning a pair of controlcables, a pair of pulleys each of said cables, a movable wedge memberarranged for moving said pulleys to defiect said cables upon movement ofsaid wedge, and a double acting power applicator connected to and foroperating said wedge member.

13. In an apparatus for automatically tensioncables, a pair of pulleyseach bearing against one of said cables, a movable wedge member arrangedfor spreading said pulleys to` deflect said cables upon movement of`said wedge, and a double acting power applicator 2o 7. An automaticcable tensioning apparatus for voperated by the pressure connected toand for operating said wedge member, said wedge member formed with awedging angle making it self locking against the pressure of saidpulleys at any point of movement.

14. In an apparatus for substantially maintaining a predeterminedtension in a tensioned operating cable, power means for applying orreleasing the tension in said cable, movable means deyiiecting thetensioned cable from a straight run at a point intermediate its length,and means of the deflection of the cable at said point arranged tocontrol the application of said power means for increasing the tensionin the cable when the pressure of said deflection falls below apredetermined value, and

vice versa.-

15. In an apparatus for substantially maintaining a predeterminedtension in a tensioned operating cable, movable power, operated means Afor defiecting said tensioned cable at a first point 10. In theconstruction set out in claim 6, vthe more or less from a straight runfor thereby varying its tension, second movable means acting under apredetermined force defiecting said cable slightly at a second point inits run, and means operated by the movement of vsaid second movablemeans through any controlling the application of said power operatedmeans for defiecting said cable more at said first point as thedeflection of the cable at said second 'point becomes greaterand -viceversa.

16. In an apparatus for substantially main-` taining a predeterminedtension in a tensioned operating cable, movable power operated means fordefiecting said tensioned cable at a iirst point more or less from astraight run for thereby varying its tension, second movable meansacting under a predetermined force defiecting said cable slightly at asecond point in its run, and means operated by the movement of saidsecond movable means through any varying tensio of said cablecontrolling the application of said power operated means for defiectingsaid cable more at said `first point as the deflection of the cable atsaid second point becomes greater and vice versa, and means for varyingthe force applied to said second movable means.

17. In a structure as set out in claim 5, means compensating for unequaldeflection of said cables.

JOHN STURGESS.

varying tension of said cable

